How much and where in the body HIV remains in patients on antiretroviral therapy (ART) has not been conclusively established even though small studies that sample accessible tissues like peripheral lymph nodes and gut biopsies from living patients on ART suggest that the concentration of infected cells is much higher in gut and lymph nodes than in Tcells in blood. The virus remaining is important because it requires that patients remain on antiviral drugs for life and it may also be the cause of the increased cardiovascular, renal, neurological, hepatic and malignant disease experienced by HIV+ patients in spite of ART. Autopsy studies would allow more comprehensive sampling but are frequently confounded because many patients nearing death stop their antiretroviral drugs or have such altered physiologic functions (metabolic, hepatic, renal, GI) that it is hard to know how antiviral effects might also be altered. In the current proposal we will take advantage of a unique partnership between the study investigators and the San Francisco Office of the Medical Examiner to study patients who die suddenly and don't go through a perimortem period when they might not receive consistent antiretroviral treatment. We will sample multiple regions of brain, different lymph nodes, liver, lung, spleen and GI mucosa and measure both HIV DNA and different forms of HIV RNA that correspond to latent infection or to productive infection by HIV. This will test the hypothesis that hotspots exist in the body where a focus of HIV infection or pronounced viral production is occurring. We will also measure concentrations of antiretroviral drugs in the hair and tissues from these subjects to determine first that the subjecs were indeed achieving adequate levels of antiretroviral drugs before death and second to explore whether lower levels of antiretroviral drugs in some tissues could account for local increases in residual virus and virus replication. To validate the relationship between hair, gut mucosa and the more commonly measured serum levels of antiretroviral drugs, we will also obtain samples from some living volunteer subjects on ART. Finally, we will perform sequence analysis of the HIV envelope gene and assays for drug resistance variants present in different tissues to determine the composition of the viral populations at the different sites and to see whether those viral genetic patterns are likely to arise from local virus replication, expansion of particular populations of infected cells or through trafficking of infected cells between different anatomic sites. When these studies are complete we will have a much more complete picture of the whole body reservoirs of HIV in patients on ART and may have uncovered additional clues about how tissue reservoirs are maintained that may help in developing new strategies to eliminate them.